Paper manufacture



wet.

Patented Apr. 9, 1935 PATENT OFFICE PAPER MANUFACTURE Herman Reed Harrigan,

John Milton Krauss,

signers to District of Columbia Paper ghevy Chaseb M125, and ashington, as- Manufacturing Company, Washington, D. 0., a corporation of Virgima No Drawing. Application March 1, 1932; Serial No. 596,150

2 Claims.

This invention relates to an absorbent paper and method for making the same, and more particularly to a paper having absorbent qualities which will maintain a high tensile strength when It is common knowledge that absorbent papers, when moistened, have a lower tensile strength than when they are dry. When it is desired to impregnate such a paper 'with a material in solution or suspension, it is important that the tensile strength of the paper be suflicient to permit of the tensioning of the sheet while it is passing through the aqueous impregnating bath. There has been considerable difiiculty in obtaining suificient' tensile strength in such a paper to withstand these conditions, without sacrificing other essential properties such as the absorbtive quality thereof.

The object of the invention is to produce an absorbent paper having suilicient tensile strength, when moistened, to be placed under tension in passing it through an aqueous impregnating bath. A further object of the invention is to produce an absorbtive paper of high tensile strength. And further objects of the invention are to pro,- duce an increasein tensile strength of an absorbtive paper without sacrificing other properties, and the production of a process by which such a paper maybe made.

Further objects and advantages of the invention will appear in the following description, and the novel features thereof will be particularly pointed out inthe appended claims.

The absorbent sheet to which high tensile strength is to be given, is passed through an aqueous solution of glue and formaldehyde, and dried. It has been found that the aqueous glueformaldehyde bath which will produce satisfactory results contains of a pound of animal glue and three liquid ounces of 37% formaldehyde solution per gallon. While these proportions have been found most desirable, it will be appreciated that they are indicative only, and that proportions at variance with these maybe used with good results.

Immediately after this treatment, the ababsorbent sheet shows a greatly increased wet tensile strength. This becomes considerably higher-on ageing; in some cases it will show a 200% increase after several days, that is a tensile strength approximately three times that of untreated paper.

In this method, advantage is taken of the facts, ((1) that if the concentration of the glue solution is not,tieyond a certain limit, the porosity of the sheet will not be affected, and (b) when glue and formaldehyde are mixed in aqueous solution in substantially the above proportions and applied to the sheet, they gradually combine to form a compound insoluble in water.

When theconcentration of the formaldehydeglue solution is too high, it becomes viscous too rapidly to be used. The concentration and proportions of the ingredients herein noted are sufficient that the working life of the solution is long enough so as to be handledeasily, and that when it is applied to the'sheet as described, it is sufliciently insoluble in water to give the necessary increase in wet tensile strength, and no difflculties are experienced in impregnating .the sheet.

. It will be appreciated that the lack of tensile strength in absorbent paper is due to the relatively short fibers of which this'type of paper is made, and that the glue is used in making the paper to produce an adherence between the fibers. Glue alone, however, would not produce the result because it is so readily soluble in water and the tensile strength of absorbent papers is greatly decreased immediately upon the application of aqueous solutions. The addition of formaldehyde, in a suitable proportion, makes the glue insoluble in water, and thereby preserves the tensile strength of the absorbent paper for a sufficient length of time to enable it to. be passed through an, impregnating bath.

The impregnating bath, to which reference has been repeatedly made, is any bath containing a material which it is desired to incorporate in the paper for any purpose. It will be appreciated that paper is used as the base of many manufactured materials.

We claim:

l 1. The process of paper making, comprising the selection of an absorbent paper and the application thereto of an aqueous solution of glue and formaldehyde, mixed in the proportions of pound of animal glue to 3 liquid ounces of 37% formaldehyde solution per gallon of water.

2. As a newarticle of manufacture, the prodnot of the method of claim 1, being an absorbent paper possessing high tensile strength, comprising fibers of such length as to maintain absorbtiveness, and a glue of relatively low solubility in aqueous loading solutions, due to the presence of a relatively small quantity of formaldehyde. r

HERMAN REED HARRIGAN. JOHN MILTON KRAUSS. 

